In the metallurgical processing of ores it is often necessary to separate the ores themselves or admixtures as well as intermediate products and final products into individual particle size fractions having the same composition or different compositions. This separation often involves a considerable structural and energy expenditure, which must be minimized.
It is known to effect the separation on a plurality of linearly vibrating screens, which are arranged one over the other and have inclinations which increase from top to bottom whereas the widths of the mesh openings decrease from top to bottom and the width of the mesh openings of each screen is 2 to 15 times larger than the desired parting size. In such case, the material to be separated is fed onto the uppermost screen at the upper end thereof, the coarser solids are deflected in the direction of inclination of the screen, the finer particles initially fall through freely and on screens having smaller mesh openings are also deflected in the direction of the inclination of the screens, the coarsest solids fraction is withdrawn as overflow from the uppermost screen, finer solids fractions are withdrawn as overflow from following screens, and solids which have passed through all screens are withdrawn as a finest fraction (U.S. Pat. No. 2,572,177; "Aufbereitungstechnik," No. 2, 1975, pages 72-75). Whereas that process enables a separation into particle size fractions and involves only a small structural and energy expenditure, it does not enable a separation dependent on the particle size and composition of solids or a recovery of a specified particle size fraction which is virtually free from finest solids.
It is also known to separate solids into particle size fractions on a plurality of inclined plates which are vibrated and have vertically aligned openings which are equal in size and spaced predetermined distances apart. To effect a separation, a gas stream is blown from the lower end of the plates to the upper end thereof so that fine-grained solids on the plates and between the plates are entrained toward the upper end of the plates (British Patent Specification No. 899,449). That process does not enable a separation into exactly defined particle size fractions and results in a relatively small throughput. The large air requirement results in a high energy expenditure, and a separation into fractions differing in composition is not possible.
It is also known to effect a separation on screens through which air flows from below and/or above (British Patent Specification No. 484,757; Opened German Specification No. 2,311,308). Whereas that process enables a separation into two fractions which differ greatly in particle size or a separation into fractions differing in composition, it does not enable a separation into more than two particle size fractions differing in composition or a recovery of a specified particle size fraction which is virtually free from the finest solids.